public partial class _Default : Page
 {
     protected void Page_Load(object sender, EventArgs e)
     {
         Button1.Click += Button1_Click;
         atpForm.AfterRender += AtpForm_AfterRender;
         atpForm.BeforeRender += AtpForm_BeforeRender;
     }

     private void AtpForm_BeforeRender(object sender, EventArgs e)
     {
         Console.WriteLine("debug breakpoint placeholder");
     }

     private void AtpForm_AfterRender(object sender, EventArgs e)
     {
         var pdfResult = (HtmlToPdfResult)atpForm.Result;
         string path = System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "output.pdf");
         pdfResult.PdfDocument.Save(path);
     }

     private void Button1_Click(object sender, EventArgs e)
     {
         Session["TestValue"] = "The quick brown fox";
         EO.Pdf.HtmlToPdf.Options.VisibleElementIds = "print-2881";
         atpForm.RenderAsPDF(false);
         Response.Redirect("About.aspx", false);
     }
 }

<section id="print-2881" class="col-md-4" aria-labelledby="librariesTitle">
      <h2 id="librariesTitle">Get more libraries</h2>
      <p>
          NuGet is a free Visual Studio extension that makes it easy to add, remove, and update libraries and tools in Visual Studio projects.
      </p>
      <p>
          <a class="btn btn-default" href="https://go.microsoft.com/fwlink/?LinkId=301949">Learn more »</a>
      </p>
  </section>